Abrasive wheel



July 25, 1939.

ABRAS I VE WHEEL Original Filed Aug. 12, 1935 E. VAN DER PYL Re. 21,165'

:EDWARD l/A/v DER-PYL Reissued July 25, 1939 tion of MassachusettsOriginal No. 2,072,051, dated February 23, 1931', Serial No. 35,881,August 12, 1935. Application for reissue April 28, 1938, Serial No.204,906

5 Claims. (Cl. 51-280) The invention relates to abrasive wheels and amethod of making the same.

One object of the invention is to provide a low melting point metallicbond for diamonds. Another object of.the invention is to provide agrinding wheel for grinding very hard substances. Another object of theinvention is to provide a grinding wheel comprising very hard grain anda bond suitable therefor. Another object of the invention is to providea bond for diamond abrasive from which the diamonds may be, recovered atsmall expense and without destruction of thediamonds. Another object ofthe invention is to provide a method of bonding carbonaceous;grain whichis effective and which may be carried out without burning the grain.Other objects willbe in part obvious or in part pointed out hereinafter.

The invention accordingly consists in the features of construction,combinations of elements, and arrangements of parts, and in the severalsteps and relation and order of each ofsaid steps to one or more of theothers thereof, all as will be illustrativeiy described herein, and thescope of the application of which will be indicated in the followingclaims.

In the accompanying drawing, in which is shown one of various possibleembodiments of the mechanical features of this invention, i

Fig. 1 is a plan view of a grinding wheel constructed in accordance withcertain features of the invention,

Fig. 2 is a cross sectional view on the line 2-2 of Fig. 1.

According to the preferred method of carrying out my invention, Iprovide diamond-grit inflnely divided or grain form. Diamond grit which,because of its extreme hardness and its other qualities, constitutesprobably the best abrasive substance known, exists in a formcommercially known as bort"' which'is commercially available insuflicient quantities and at such prices that it may be used for themanufacture of grinding wheels and other abrasive bodies. 'Whilebort isexpensive, nevertheless on account of the great superiority of thediamond for abradant purposes, the wheel formed thereof has manypractical uses and advantages.

Also, in the preferred embodiment ofmy invention, I provide bond in theform of. a powdered ,alloy. Although such powdered bond might be amixture of two or more metallic powders, I prefe to proceed as follows.

Selecting two or more metals according to considerations hereinafter setiorth I put them togather in a melting pot in the proportions desiredand melt them together. I then cast ingots crush by means of crushingrollers or the like until the allow is in powdered form of the desiredmesh size.

With the powdered metallic bond of the type indicated 1 mix in theneighborhood of between 25% and 50% by volume of diamond bort in a gritsize of between mesh and 500 mesh, for example. Mesh size of the bortselected will depend upon the abrading operation that the wheel of thealloy in sand molds. These ingots I then is to perform, and my inventionhas no limitations in this .respec't,.in so much as grinding, polishingand lapping operations differ vastly among themselves. For the finerpolishing or lapping operations, finer grit size of bort will be used.The mesh size of the metallic bond may also vary between wide limits; Imerely note that using mesh diamondgrit, powdered bond of 200 mesh ishighly practical, but other mesh .sizes of the bond may be used evenwiththe given size of diamond grit.

' The mixing of the grit with the bond maybe accomplished manually, foralthough machine methods might be used, the bort or diamond dust isso'valuable as to dictate care in the mixing to avoid loss of diamond.Setting apart a measured or desired quantity of mixed bond and bort, Iplace it in a mold. This mold may take any form, for although I amdescribing the invention in connection with the manufacture of a wheel,other abrasive bodies are to be deemed ineluded. In case the abrasivebody is a wheel, in most cases it will have a central hole for mounting'upon an arbor or the like, and accordingly in such cases the shape ofthe mold is an annulus. For the material of the mold I prefer graphite,on account of its many desirable properties, such as that it may beeasily destroyed to remove the formed wheel; it has an aflinity foroxygen thus inhibiting oxidation of the materials of the wheel; it isreasonably inexpensive; it may be easily machined into desired form orshape; it will not melt and will not go to pieces under any temperatureswhich I contemplate using,

Having placed the desired quantity of mxed rain and bond in the moldselected, I apply heat and pressure. Within the limits of my inventionthe pressure range is wide. and the heat employed is such as to causesintering of the bond at the pressure employed or under the conditionsof intimate union achieved. For example, I may cold press the bond andabrasive grain, heating the substance thereafter. In such cases I mightwith plunger and pressure mechanism, heating or 2%, of beryllium(glucinium).

the formed or 'green" wheel on a "bat". The union of the metallic grainafter it has been pressed is such that it may be formed into apractically integral mass which will tightly hold the abrasive bodies byheat treating at a temperature which does not completely melt to aliquid state but sinters. The separate pressing and heating of thebodies has the advantage that a simpler apparatus and a cheaper methodmay be employed. However, in certain cases the heat and pressure may beapplied simultaneously.

Considering now the bond employed according to my invention, Ipreferably use an alloy of copper. With the copper I alloy another metalwhich produces an alloy harder and more brittle than copper. I desirethe bond to hold the diamonds firmly, to be tough and enough so that thediamonds will not rip out, and nevertheless at a certain pressure andresistance to go to pieces rather than glaze. It is desirable that thebond should crumble off in little bits or fine frag- .rnents so as toexpose new cutting edges of the diamond from time to time, and an alloyor metal which can be crushed to powdered form may have the desiredcharacteristics. Such an alloy is brittle and may be characterized asfriable. I give below examples of specific alloys which I may use.

Example 1 Example 2 I make an alloy of copper and nickel, 35-50% ofcopper and 65-50% of nickel. This also has 'brittle characteristics andis tough. It melts at around 1200 C., but I may use the precautionshereinafter referred to to prevent oxidation of the diamond or the bond.

Example 3 I make an alloy comprising approximately 85 copper with 15%aluminum. This melts at around 1050 C. and has brittle characteristicsbut is fairly tough.

Example 4 I make an alloy of copper and manganese,-

65% or more of copper and 35-20% of manganese. This melts at 900 C. andhas the properties of toughness and brittleness desired.

Example 5 I use nearly pure copper but mix in with it a very smallproportion, from a trace to 1% Copper melts at 1065" C. or thereabouts.

It is advantageous to take certain precautions against burning of thediamonds in the case of the alloys which sinter at the highertemperatures, in example above 900 C. The use of a graphitemold orcontainer during the heating operation is 'such a precaution. However,even whena graphite mold is'used', and more especially so when it isnot,. it will be well to heatthe body in a non-oxidizing atmosphere,such as nitrogen or hydrogen. I have also foundthat a small amount ofaluminum, silicon or magnesium may be introduced into the bond,preferably asseparate distinct metallic particles, that is not in analloy state, which will inhibit oxidation of brittle as possible for thespecific alloy used and brittleness is enhanced by quenching theabrasive body when still hot from the heat treatment.

One marked advantage of a wheel constructed according to the inventionlies in the fact that, when produced in annular form, it may be readilyunited to a central disk. Diamond grinding wheels are, under presentmarket conditions, expensive,- whatever the bond used, owing simply tothe high price of bort, and accordingly it is highly desirable to wasteas little of the diamond as is possible. Inthe case of any grindingwheel which is thin relative to its diameter, the central part willgenerally not be used for abrading. Accordingly, in the case of diamondwheels it is preferred to form the central part in the form of anon-grinding disk or annulus. While a small internal grindingwheel,having alength on the order of half its diameter, may comprise 100%grinding substance and be attached by mounting directly upon a spindle,in the case of a cuttingoif wheel or a large sized wheel for thegrindingof the. cemented tungsten carbides and other hard substances, it isgenerally found economical to secure what amounts to an annular band ofdiamond grinding material to a central diskhaving hole therein.Therefore, ,a distinct problem has arisen in attaching the inside of theannular band of grinding substance to the periphery of the centralsupporting disk. It the union between the parts is weak, fracture willresult and this destroys the grinding wheel which may have a marketvalue in the neighborhood, of from $50 According tothe presentinvention, with diamond bonded with metallic bond'as' disclosed in theforegoing description, I may provide a thin aluminum disk, or a disk 01any other metal, and form my grinding substance inthe shapeof an annularband whose inner diameter is the same as the outside diameter of thedisk. I may then unite the disk to the grinding band by brazing,soldering, preferably with silver solder, or by any other metallurgicaloperation for integrally uniting metals, such as welding or the like,and the result is an integral structure of central supporting metallicdiskhaving an annular band 01' grinding substance on its peripheryincluding diamond grain bonded in a metal bond. For cutting-oil wheelsand the like, the central support-' ing disk should be no thicker thanthe annular band of grinding material. Referring now to the drawing, Iprovide a central disk III which may be made of any suitable metal. suchas alu- ,Although I have notedthroughout diamond as the abrasive grit,certain advantages inhere in the combination of the bondspecified withboron carbide grit. Boron carbide is an expensive abrasive grit,although not as expensive as diamond bort. Furthermore, boron carbide aswell as diamond should not be exposed to high temperatures, or if it isonly for a short time and with suitable precautions such as indicated,in order to avoid oxidation and other chemical changes. The bondsdescribed herein are all of them reasonably low melting point bonds, andtheyfuse or sinter at a somewhat low temperature when under pressure orwhen the particles are in intimate contact as described, and accordinglythese bonds are very suitable for the bonding of diamond and othercarbonaceous substances such as boron carbide. The bonds of theinvention are more in the nature of a matrix than the common vitrifiedbonds, and they are harder and tougher than the artificial resinousbonds, and have properties different from those of a rubber bond, andthe properties of the bonds of this invention are highly desirable incombination with grain of extreme hardness such as diamond and boroncarbide, on Mohs scale extension l5 and I4 respectively.

successfully achieved. As various possible embodiments might be made ofthe mechanical features of the above invention and as they are hereindescribed might be varied in various parts, all

without departing from the scope of the invention, it is to beunderstood that all matter hereinbefore set forth is to be interpretedas illustra-' 2. An abrasive body comprising diamond grain and a copperaluminum bond.

3. An abrasive body comprising diamond grain and a copper tin bond.

4. An abrasive body comprising diamond grain and a metallic bondconsisting 01 copper and an additional metal adapted to impartfriableness to the copper and comprising one of the group consisting ofnickel, aluminum, manganese, tin and beryllium, the proportion of theadditional metal being such as will impart the friableness.

5. A grinding wheel comprising a metal disk integrally united to anannular outside band comprising diamond grainbonded with metal, both thedisk and the band including aluminum.

- EDWARD VAN DER PYL.

